Patent GB-811111-A (GB)
Title: Apparatus for cyclically monitoring potentials at a number of stations
Inventor: BOWEN DENNIS DAWES
IPC: G01K1/02
Filed: 1955-06-09
Abstract: 811,111. Voltage measurement. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. May 31, 1956 [June 9, 1955; Sept. 7, 1955], Nos. 16557/55 and 25579/55. Class 37. [Also in Group XXXVIII] Apparatus cyclically monitoring electric potentials (e.g. derived from thermocouples) at a number of stations comprises means for cyclically scanning the plural stations to derive a sequence of corresponding electric potentials, means comparing such potentials each with a reference potential in turn to derive a sequence of difference potentials each corresponding to a station in the scanning cycle, and an amplifier for such difference potentials, the output of which is applied to means for detecting when such potentials fall outside a predetermined band of amplitudes, and means for recording the identity of the stations giving rise to such potentials outside the band. Thermocouples 10 (Fig. 1) develop unidirectional voltages corresponding to discrete temperatures which are combined with a preset voltage from D.C. energized potentiometer 22 defining a standard temperature, and each difference value is sequentially selected by the wiper of uniselector 17 for application to a vibrator 20 generating alternating voltages dependent in amplitude and phase sense on the corresponding difference voltage, which after push-pull amplification are rectified by double diode 26 (Fig. 2), feeding the first grid of a double triode 35 connected as a trigger circuit in which thes econd grid bias is controlled by variable resistance 56 of a potentiometer circuit and the second anode circuit contains a relay ALR operated when the trigger circuit turns over at an input level set by resistance 56. The rectifier output also feeds a similar double triode 39 in a trigger circuit turning over at an input level set by variable resistance 46 to operate second anode relay AR, while the first anode is directly connected to the grids of both sections of a double triode 43 ; variably biased by potentiometric resistances 47, 48 and having the cathode connected to that of double triode 39, while the respective anode circuits contain relays BR, CR which operate at rectified input levels set by resistances 47, 48. Double triode multivibrator 31, having a frequency adjusting feed-back variable capacitance 50 and a normally closed disabling switch 51 across an additional cathode load, pulses relay UMB in the first anode circuit to impulse the uniselector magnet UDM (Fig. 3), so that the successive thermocouple outputs are scanned, while a portion of the first anode voltage of the multivibrator (shunted by parallel resistance/capacitance circuit 53, 54) is superimposed on the rectified input signal, which is also capacitance coupled to a cathode-ray tuning indicator 30 having normally open disabling switch 40 in its cathode return. The anodes of double diode 26 are connected to a phase-sensitive rectifier 28 (Fig. 1), energizing a relay PSR to operate only when a predetermined anode of the rectifier conducts but not otherwise. In operation, resistance 22 is set to a required value representing the mid-point of a selected temperature range by reversing switch 32 to disconnect the uniselector and connect a known voltage source 34, closing switch 40 to energize the tuning indicator 30 and adjusting for null indication. Resistances 56, 46, 47, 48 are preset so that relays ALR, AR, BR, CR operate successively for graduated predetermined deviations of thermocouple temperature in either sense from the mid-range value, and the phase-sensitive rectifier 28 is adjusted so that relay PSR operates when any temperature falls below the mid-range value. Switches 32, 40 are restored and switch 51 closed so that the uniselector impulses and selects difference voltages from successive thermocouples at a frequency determined by variable capacitance 50. So long as the temperatures remain within a predetermined band the circuits of valves 35, 39, 43 remain stable, but any deviation in either sense causes valve 35 to turn over and operate relay ALR, operating relay DR (Fig. 3) to energize over contact DR1 an electromagnetic printing punch SM geared to the uniselector spindle, which impresses the number of the particular thermocouple on a paper tape (Fig. 3A, not shown). A fall in temperature from the mid-range value causes phase-sensitive rectifier 28 to operate relay PSR, which when relay DR has operated energizes printing punch PM over contact PSR1 to impress a phase mark on the tape against the appropriate thermocouple number. A further degree of temperature deviation causes valve 39 to turn over and operate relay AR, which energizes printing punch AM over contact AR1, unless relays BR, CR have been operated, to impress a corresponding mark on the tape, while successive further degrees of deviation cause the first and second triodes of valve 43 to operate relays BR, CR to respectively close contact BR1 (if relay CR is inoperative) and contact CR1 to energize printing punches BM, CM to impress distinctive marks on the tape against the appropriate thermocouple number. Between multivibrator strokes (and steps of the uniselector) the first anode of double triode 31 conducts and imposes a negative pulse on the first grids of double triodes 35, 39 to disable them for a short time dependent on the values of RC circuit 53, 54, during which relay UMR operates, steps the uniselector and releases, so that spurious input pulses are prevented from causing false records. A time record from a local clock is continuously impressed on the tape. Each or any selected thermocouple may have a distinctive preset voltage from plural potentiometers 22 selected by a further bank of the uniselector. In a modification (Figs. 4A-4D), 245 thermojunctions 70 are respectively connected to the contacts of a 5-bank uniselector 75 whose five wipers B1-B5 are switchably selected on successive rotations by rotary switch 80 operated by magnet 78 impulsed on closure of the last contact 79 of each bank. The common thermocouple return 82 receives an adjustable preset unidirectional voltage from the slider of a '' fine adjustment " potentiometer 97 energized from a differential " coarse adjustment " potentiometer 97 energized from a differential " coarse adjustment " potentiometer 96 energized from a temperature compensated bridge circuit 92, 93, 94, 95, supplied with a unidirectional voltage from a neon tube stabilizer 87. Each resultant difference voltage is applied to 50 c.p.s. vibrator 84 generating an alternating voltage, corresponding in amplitude and phase sense, at the output AB of transformer 102, which after amplification by transformer coupled pentodes 104, 105 is rectified by double diode 107 from which connections E, F derive a unidirectional voltage from the cathode and an alternating voltage from a single diode anode. Connection E feeds a double triode trigger valve 115 having relay AR in the normally conducting second anode circuit, which cuts off at an input voltage controlled by the second grid variable biasing resistance 120, while the first anode is directly coupled to the first section of double triode 118 having relay LR in its normally conducting anode circuit, which cuts off at an input voltage determined by the variable grid-biasing resistance 123. The second triode section of 118 receives in its grid the alternating voltage on connection F and a reference alternating voltage on its cathode from transformer secondary 130, to operate as a phase-sensitive rectifier having a polarized relay PR between its resistance loaded anode and a variable potentiometer 125, 126 across the H.T. supply. A cathode-ray tuning indicator 140 having a normally open disabling switch 113 in its cathode is connected to the rectified output of a double diode 107. A double triode multivibrator 127, having relay RR in its first anode circuit and its frequency established by feedback capacitance 131 switchably in parallel with capacitance 132, has its cathode connected over a normally open disabling switch 128 in parallel with the cathode of amplifier pentode 105 to the return resistance 146. In operation, the uniselector at its starting point selects either a first thermocouple at a standard temperature or a corresponding reference voltage. Switch 128 is opened, switch 113 is closed, and potentiometers 96, 97 adjusted for null of the tuning indicator 140. Switches 128, 113 are then reversed so that the multivibrator operates at the required frequency to pulse relay RR impulsing relay SR so that the uniselector steps to connect each thermocouple successively, while the electromagnetic counter CR is simultaneously impulsed to identify each couple. At each impulse, a positive cathode pulse is applied to pentode 105 whereby it is cut off, so that false signals during thermocouple changeover are suppressed, and the difference voltage derived from each thermocouple due to any temperature deviation from standard is converted to a corresponding alternating voltage of corresponding amplitude and phase sense which after rectification triggers the second section of double triode 115 to cut off and release relay AR if the temperature deviation exceeds a value set by resistance 120. Contacts AR1 close, relay DR operates (after a 20 millisecond delay to eliminate false signalling due to the inter-thermocouple cut off of pentode 105) and contact DR1 closes to energize magnet IR to impress type wheels driven by counter CR to record the thermocouple number on a paper tape (Fig. 4E, not shown), traversed one step by magnet PF on each release of relay DR. A larger temperature deviation exceeding a value set by resistance 123 cuts off the first section of double triode 118 so that relay LR releases, closing contact LR1 to energize magnet EM, which forces a corresponding punch 137 through the paper (Fig. 4E, not shown). According to the phase sense of the alternating signal from one anode of double dio